1. Field of the Invention
The present invention relates to a data recording medium and, more particularly, to an optical card having track identifying data disposed alternately on tracks and a recording/reproducing apparatus therefor.
2. Description of the Related Art
An optical card is a kind of data recording medium. The optical card is generally rectangular in shape and has a data recording area on its major surface. On the data recording area a plurality of guide lines are formed parallel to one another in the direction of the long side of the card. A portion between adjacent guide lines is called a track on which data to be later reproduced is recorded. Further, track-identifying address data is recorded at one end of each track prior to recording data for later reproduction. To record or reproduce data, address data is read first so as to determine whether the corresponding track is a read/write track for recording or reproducing.
The recording/reproducing apparatus adapted to record data on or reproduce data from the optical card comprises an optical system for directing a laser beam, adapted for recording or reproducing data, onto the data recording area of the card, and a carrying system for carrying the card. The optical system is moved by a predetermined distance in the direction of the short side width of the card in order for a laser-beam spot to gain access to a destination track. After the access to the destination track, the carrying system is moved by a predetermined distance in the direction of the long side of the card in order for the spot to gain access to a destination location on the destination track. During recording or reproducing, particularly, the carrying system is frequently moved back and forth. Usually, the length of an acceleration section in which the carrying system is accelerated and the length of a deceleration section in which the carrying system is decelerated during the reciprocating motion of the carrying system are equal to each other.
With such a card as described above, address data is recorded at one end (for example, the left-hand end) of each track. Therefore, in order to record on or reproduce from the next track after the completion of recording or reproduction for one track (at this time the laser-beam spot locates at the other end, or the right-hand end of the one track), the carrying system will have to be moved so that the spot may return to the left-hand end of the next track to read address data. Thus, additional time is required to return the spot from the right-hand end of one track to the left-hand end of the next track.
To save time, there is another type of card in which address data is recorded at both ends of each track. In the case of this type of card, however, it is apparent that the data recording area is reduced because address data is recorded not only at one end of each track but also at the other end thereof.
Further, the idea that the acceleration section and the deceleration section of the card carrying system should be equal in length to each other has commonly been accepted. Therefore, the reduction of these sections, which do not contribute to the recording and reproducing of data in practice, has not been seriously considered up to now.